The operation of electric hand drills is typically controlled by means of a pull-trigger for switching on and off the motor as well as to adjust its speed/torque. The trigger incorporates an electronic operating circuitry that includes a solid-state device for switching at a variable duty cycle to control the speed/torque of the motor. While the solid-state device is non-conducting during switching, a flywheel diode allows the motor current to continue to flow. For heat dissipation, the diode is invariably located at a position away from the trigger and is connected thereto by cables, which renders the assembling process complicate.
The invention seeks to mitigate or at least alleviate such a problem by providing an improved trigger assembly.
According to the invention, there is provided a trigger assembly for controlling the operation of an electric power tool including an electric motor, comprising a base for fixing within the power tool and a trigger supported by the base for inward and outward movement, the trigger being resiliently biassed outwards. The base has a housing including an opening open to the interior of the power tool. A switch provided in the base housing is operable in response to the movement of the trigger to switch on and off the motor. An electronic operating circuitry provided in the base housing includes a solid-state device for switching at a frequency having a variable duty cycle to control the operation of the motor when the switch is closed. Also included is a flywheel diode for the motor, which is operable when the solid-state device is non-conducting while switching. The diode is supported at or adjacent the base housing opening to facilitate heat dissipation.
Preferably, the flywheel diode protrudes at least partially out of the base housing opening.
It is preferred that the flywheel diode has a body protruding partially out of the base housing opening and a pair of terminals substantially within the base housing opening.
It is further preferred that the body of the flywheel diode has an oblong shape having an axis and opposite ends from which the terminals extend, the axis lying substantially parallel to the base housing opening.
Preferably, the flywheel diode has an oblong body having an axis and opposite ends and a pair of terminals extending from the body ends respectively, the axis lying substantially parallel to the base housing opening.
Preferably, the base housing opening is substantially flat.
In a preferred embodiment, the flywheel diode has a pair of terminals, and two rigid conductors in the base housing locate the flywheel diode by its terminals.
More preferably, at least one of the terminals is press-fitted to and thus connected with the corresponding conductor.
Further more preferably, the corresponding conductor has a recess of a width marginally smaller than a cross-sectional dimension of said at least one terminal, such that the terminal can be laterally press-fitted into the recess and thus connected with the conductor.
Further more preferably, the recess comprises a cutout having an opening of said width.
It is further preferred that said at least one conductor generally extends at right angles to the base housing opening, and the recess opens in a direction transversely to the general extent of the conductor.
The invention also provides an electric power tool including an electric motor and the aforesaid trigger assembly.
In one example, the electric power tool is an electric hand drill.